Particulate reagents are frequently used in bioassays. However, use of these reagents is often hampered by nonspecific binding of biological molecules to the particles, resulting in false positives, or apparent high background binding, leading to inaccurate detection and poor quantitation and purification. Numerous efforts have been made to reduce nonspecific binding, typically involving covalently attaching gelatin, dextrans or modified dextrans or the like to the particles to provide a hydrophilic layer to reduce nonspecific adsorption or binding of unwanted biological molecules to the particles. The nonspecific binding of biomolecules is reputed to be minimized by the dextran layer due to its essentially uncharged and hydrophilic character and the mobility of the attached dextran chains.
For example, U.S. Pat. Nos. 5,639,620 and 5,776,706 to Siiman purport to describe gelatin and aminodextran coated polymer core particles, including the preparation of aminodextrans having varying amounts of amine groups, and a method of crosslinking gelatin and aminodextran without the use of a stabilizer. The method is described as producing colloidal particles having a surface with hydrophilic properties. Siiman states that the polymer and antibody layers on the particles should be covalently bound to each other in order to reduce dissociation and conformational changes, and that this can be accomplished by preparing particles having a biodegradable coating to which can be attached pendent biological substances, such as monoclonal antibodies. Similarly, U.S. Pat. No. 5,707,877 to Siiman purports to describe discrete colloidal particles having a solid core coated with a first layer of a water soluble gelatin and a second layer of an aminodextran, said coating being crosslinked or fixed by the action of a chemical crosslinking agent and having a plurality of pendent functional groups. The pendent functional groups are described as having terminal aldehyde or carboxylate groups, amine groups, sulfhydryl groups or maleimidyl groups, and polyclonal or monoclonal antibodies, and the core is described as being metallic particles formed in gelatin solution or preformed particles which are then coated with the gelatin. Siiman further describes discrete colloidal particles having pendent biological functional groups such as polyclonal and monoclonal antibodies covalently attached to the crosslinked second aminodextran layer by means of a heterobifunctional crosslinking agent, which purportedly acts as a bridging group between the biological substance or functional group and the crosslinked gelatin or aminodextran. Siiman further describes a process for coating a solid core material which has a hydrophobic surface with first gelatin layer and a second aminodextran layer, crosslinking the adsorbed outer coating and derivatizing the crosslinked coating to obtain a product having a desired reactive species covalently bound to said crosslinked coating surface.
In addition, U.S. Pat. No. 5,466,609 to Siiman purports to describe colloidal particles having a core material and a gelatin/aminodextran coating, said coating being crosslinked or fixed by the action of a chemical crosslinking agent and having a plurality of pendent functional groups. Biological substances or molecules, especially monoclonal antibodies, allegedly may be covalently attached to the crosslinked second aminodextran layer by means of a heterobifunctional crosslinking agent so as to enable advantageous use of said antibody functionalized particles in biological separations and assays. The heterobifunctional crosslinking agent purportedly acts as a bridging group between the biological substance or functional group and the crosslinked gelatin or aminodextran. The monoclonal antibody containing particles are reported to be useful in a variety of positive and negative biological assays.
U.S. Pat. No. 6,231,982 to Wang describes the preparation of magnetic and non-magnetic particles coated with a polyaldehyde dextran material and a process for making the same. The particles are allegedly prepared by first oxidizing dextran with selected oxidizing agents to obtain a dextran-derived substance having a plurality of pendent aldehyde groups, and coupling the dextran-derived substance to a magnetic or non-magnetic particle having pendent amino groups or other functional groups reactive with aldehyde groups to obtain a dextran-coated particle. The polyaldehyde dextran coated particles are alleged to be suitable for use in immunological assays and exhibit a reduced matrix effect in such assays when compared to conventional particles lacking a polyaldehyde dextran coating.
U.S. Pat. No. 5,576,220 to Hudson describes methods and systems of unhindered construction and display of tethered organic ligand molecules, and more particularly to preparation and use of thin film, substantially non-crosslinked hydrophilic polar multifunctionalized polymers (HPMP) anchored to a variety of functionalized substrates so that the HPMP forms a thin film matrix layer providing a highly hydrated high dielectric environment equivalent to an aqueous solution, for affinity binding of ligands to target molecules. The HPMP thin film is allegedly 200-2000 Å thick, and reportedly can be any biocompatible substantially uncrosslinked high molecular weight highly soluble polysaccharide, such as high molecular weight dextrans. The ligands are allegedly singly tethered to the HPMP by a “permanent” strong covalent bond so that subsequent displacement of the target molecule does not also displace the ligand from the HPMP.
U.S. Pat. No. 5,248,772 to Siiman purports to describe the use of aminodextrans in the formation and coating of colloidal metal(O) particles, and the formation of colloidal metal dispersions using aminodextrans as reductants and protective agents. After crosslinking the aminodextran coating using a crosslinking agent, the coated particles reportedly can be used to covalently bind proteins.
U.S. Pat. No. 7,169,618 to Skold purports to describe a method for separating material using colloidal magnetizable aggregates optionally silanized and coated with polysaccharides having pendant functional groups to which is linked a member of a specific binding pair.
U.S. Pat. No. 7,172,906 to Teng purports to describe a method for reducing nonspecific binding in a binding assay for the determination of an analyte in a sample where one of the reagents for conducting the binding assay comprises a solid support comprising a polysaccharide. The method comprises including in an assay medium for conducting the binding assay a soluble compound comprising a protein linked to a polysaccharide.
U.S. Pat. No. 7,179,660 to Kirakossian purports to describe a polysaccharide coated carrier having a coating of at least two successive layers of polysaccharide, and a layering method for coating by employing sequential coating with oppositely charged polysaccharides. In certain embodiments, the pendent functional groups reportedly are used to bind specific binding partners to the surface coating of the carrier.
Accordingly, researchers have devised methods for attaching coatings to particles and for attaching ligands or members of binding pairs to the attached coatings on the particles. However, there remains a need for improved methods for preparing particles for diagnostic assays and the like having reduced nonspecific binding.